As long as oil drilling has existed, different well service tools have been used with the objective of delivering a powerful blow for carrying out a certain operation, for example, in the collecting of various equipments in the well, breaking of glass plugs in the well, in the opening or closing of a production valve in the well or similar operations.
Initially, the so called Spang jars or tubular jars were used, which originally are composed of a steel body that is accelerated a certain distance before it abruptly stops mechanically and thereby delivers a hammering energy. These are commonly used where there is a need for one blow only of relatively little force as the acceleration is normally manual in that a person pulls on a taut wire.
More refined versions have gradually been introduced where one has either a typical mechanical jar or hydraulic jar where a much higher kinetic energy can be pre-stressed in the wire before the release. These often use a so-called accelerator fitted over itself as a spring packet that stores/accumulates the kinetic tension force energy relatively near the jar as opposed to only using the kinetic tension energy in a taut wire. The taut wire will be much slower to accelerate the jar as the wire can be many thousand meters long.
Today, primarily two kinds of jars, also called hammering tools, are used in the industry, namely mechanical and hydraulic jars. Both have advantages and disadvantages in use.
With the mechanical jars, a certain release force is pre-set, which leads to the tool delivering a certain hammering energy when it comes up to the tension force that has been pre-set. This will then deliver a blow immediately the tension force has been reached. Mechanical jars have no seals where one can close off the well pressure, but they have a simple design.
The disadvantages are that the hammering force is limited to the pre-set value before the tool went into the well and the tension release force must be set/verified with a suitable tool before use.
Hydraulic jars have the advantage in that they give an optional hammering power dependent on the pre-stressing force and that no preparations with the pre-stressing of the release force are necessary before use.
The disadvantages with the use of hydraulic jars are that these have a more complex construction; they are more expensive, require more maintenance and must be overhauled more often. In addition, there is a risk of locking the well pressure inside the tool if leakages occur. A given holding time is also required for each hammering (typically 0.5-2 min) that can result in the job taking an unnecessary long time if many blows are required to carry out the operation.
The wells that are drilled today are both longer and deeper than before. This leads to both the pressure and temperature increasing in these wells. With operations furthest down in these wells, mechanical jars will be preferred for safety reasons, although it will undoubtedly be most operationally appropriate to use hydraulic jars with the functional advantages they have.
NO20120728 shows a re-setting arrangement for cable operated hammering pipes. A mechanical hammering tool is shown where a given, but adjustable, release force, can be changed in that the sending of the tool down will rotate a circular J-slot casing/setting mechanism to the next step and thereby change the compression distance on a release spring and change the release force. The adjustment operation of the next step must be carried out manually. The J-slot casing/setting mechanism has a changing axial length position dependent on the twisting orientation. This makes it difficult to make major changes to the release force as this must go through several steps to come to the required release force. With the release, the lower trunk section will be led upwards and the trunk lock will engage with a groove in the housing, the upper trunk section comes lose from the lower trunk section and is led further up until it meets the upper edge of the housing.
U.S. Pat. No. 4,919,219 describes a mechanical hammering tool where a given, but adjustable, release force can be altered if necessary in that a downwards pushing with a given force will rotate a circular J-slot to the next step and thereby change the compression distance on a release spring and thereby also alter the release force. As with NO20120728, one must, in this publication, consciously carry out an adjustment operation to the next release step according to need. The J-slot casing/setting mechanism is rotary and has a changing axial length position dependent on the orientation of the twisting.
The present invention distinguishes itself from the prior art publications in that they have fixed release steps within a certain interval where the adjustment to the next step must be carried out physically and deliberately by the operator as opposed to the present invention where the adjustment of the release force is an integrated part of normal jar operation.
The present application is derived and developed to overcome the weaknesses of the known method and to achieve further advantages.